Large numbers of normal newborn infants are systematically exposed to a new and potentially harmful environmental agent routinely utilized for the treatment of neonatal jaundice - high intensity illumination with visible light or phototherapy - often for extended periods of time. The proposed research project will enable us to further characterize the DNA-modifying activity of phototherapy for eukaryotic cells in culture by analyzing the physical chemical properties of DNA isolated from cells exposed to phototherapy in vitro. We will then determine if similar DNA-modification occurs in animals exposed to various phototherapy regimens and determine the action spectra for these genetic effects in order to facilitate the development of a phototherapy unit effective in the treatment of hyperviliruminemia yet devoid of DNA-modifying activity.